RE: font/glyph metrics proposed wording

Benoit --

I like it, thanks.  (My prose muse seems to have been away from the office 
yesterday!)

-Lofton.

At 09:22 AM 4/29/2009 -0400, Bezaire, Benoit wrote:
>Sorry Lofton,
>
>I meant to reply yesterday, but couldn't find the time. I thought your 
>suggestions was a bit repetitive... I tried to make it shorter without 
>changing the meaning.
>
>[[[
>For the purposes of the object extent (bounding box) calculation, each 
>glyph is treated as a separate graphics element. The calculations assume 
>that all glyphs occupy their full glyph cell in both the vertical and 
>horizontal directions. Therefore, calculations assume that each glyph 
>extends to the full ascent and descent vertical font values; and to the 
>glyph's horizontal advance value. In CGM:1999 terminology, full ascent and 
>descent are known as bottom-line to the top-line (see Figure 11, CGM:1999 
>section 6.7.3.2).  For example, the font's bottom-line and top-line 
>typically correspond to the ymin/ymax values of the fontBBox item found in 
>the databases of @@WebCGM's core thirteen fonts.@@  Similarly, the full 
>horizontal extent of the glyph cell for the particular glyph -- as 
>distinct from actual drawn extents of the glyph -- corresponds to the 
>glyph's horizontal advancement value (WX) in the font databases of 
>@@WebCGM's core thirteen fonts@@.
>]]]
>
>
>----------
>From: public-webcgm-wg-request@w3.org 
>[mailto:public-webcgm-wg-request@w3.org] On Behalf Of Lofton Henderson
>Sent: Tuesday, April 28, 2009 7:01 PM
>To: WebCGM WG
>Cc: Forrest Carpenter; Robert Orosz; Ulrich Läsche
>Subject: font/glyph metrics proposed wording
>
>All --
>
>Looking at the attached below message, we chose Option 3.  In the telecon, 
>Benoit raised the question about horizontal extent of the text.  It is a 
>good one, because the answer is not totally obvious when you look in the 
>helvetica.afm file.
>
>We talked some more, and here is my draft of the changes to the current 
>(15th March) editors text.  Specifically, replace the 4th paragraph of 
>that text [1].
>[1] 
>http://www.w3.org/Graphics/WebCGM/drafts/current-editor-21/WebCGM21-DOM.html#getObjectExtent
>
>Current 4th pgph:
>
>[[[
>For the purposes of the object extent (bounding box) calculation, each 
>glyph is treated as a separate graphics element. The calculations assume 
>that all glyphs occupy their full glyph cell. In particular, the 
>calculations assume that each glyph extends vertically from the 
>bottom-line to the top-line of the font (see Figure 11, CGM:1999 section 
>6.7.3.2) -- i.e., the vertical extent of each glyph includes the full 
>ascent and descent values for the font, regardless of whether the 
>particular glyph actually has ascenders and/or descenders.
>]]]
>
>Proposed:
>
>[[[
>For the purposes of the object extent (bounding box) calculation, each 
>glyph is treated as a separate graphics element. The calculations assume 
>that all glyphs occupy their full glyph cell, in both the vertical and 
>horizontal directions. In particular, the calculations assume that each 
>glyph extends vertically from the bottom-line to the top-line of the font 
>(see Figure 11, CGM:1999 section 6.7.3.2) -- i.e., the vertical extent of 
>each glyph includes the full ascent and descent values for the font, 
>regardless of whether the particular glyph actually has ascenders and/or 
>descenders.  The font's bottom-line and top-line (full ascent and descent 
>values) typically correspond to font-metric information in the font 
>database, for example the ymin/ymax values of the fontBBox item found in 
>the databases of @@WebCGM's core thirteen fonts.@@  Similarly, the full 
>horizontal extent of the glyph cell for the particular glyph -- as 
>distinct from actual drawn extents of the glyph -- is typically found in 
>the individual glyph-metric information in the font database, for example 
>each glyph's horizontal advancement value (WX) in the font databases of 
>@@WebCGM's core thirteen fonts@@.
>]]]
>
>I admit that the language is a little awkward in places -- I'll clean it 
>up, or feel free to make suggestions for clean-up.
>
>Mainly, I want WG endorsement of the basic content -- what we're saying -- 
>and how we're presenting it ("for example").
>
>Regards,
>-Lofton.
>
>At 05:01 PM 4/27/2009 -0600, Lofton Henderson wrote:
>>Forrest has finished his action item to illustrate the font metrics:
>>[1] http://lists.oasis-open.org/archives/cgmo-webcgm/200904/msg00131.html
>>
>>Have a look at the great picture that he generated.
>>
>>This should allow the dependent tests [gOE and gOET] to go forward.
>>
>>For the spec, our question is:  what changes, if any, should go into the 
>>WebCGM spec to clarify this for future implementors?
>>
>>Options:
>>1.) none -- the existence of "FontBBox -166 -225 1000 931" in the AFM 
>>data (Helvetica in this example) should be sufficient.
>>2.) normatively add to WebCGM spec the information from the AFM for the 
>>core-13 fonts of WebCGM.
>>3.) in the WebCGM spec, informatively explain or add or point to the 
>>information from the AFM.
>>4.) other?
>>
>>We will discuss on Tuesday.
>>
>>Note that options #2 and #3 don't answer the question for any font 
>>outside of the core-13, which can be any font that has an associated FONT 
>>PROPERTIES element.  (My opinion:  those generator/viewers need to figure 
>>out and understand what is 'bottom' and what is 'top' for the "odd" 
>>fonts, just as we have figured it out for core-13).
>>
>>-Lofton.
>>
>>>X-Mailer: QUALCOMM Windows Eudora Version 5.1
>>>Date: Mon, 27 Apr 2009 16:02:18 -0600
>>>To: "'WebCGM'" <cgmo-webcgm@lists.oasis-open.org>
>>>From: Lofton Henderson <lofton@rockynet.com>
>>>Cc: David Cruikshank <dvdcruikshank@gmail.com>
>>>
>>>
>>>Forrest -- that's great!  I think your results unambiguously answer that 
>>>AFM ymin is CGM:1999 'bottom' and AFM ymax is CGM:1999 'top', for all 
>>>intents-and-purposes.
>>>
>>>Stuart -- you should be able to check/update your tests to ensure that 
>>>you're using the right numbers for 'bottom' and 'top'.
>>>
>>>All -- we will discuss on the Tuesday vF2F agenda, what (if anything) to 
>>>do about this in the WebCGM specification.  (Which has normative 
>>>reference indirectly to other bits of the AFM via CGM:1999 annex I.)
>>>
>>>Regards,
>>>-Lofton.
>>>
>>>At 01:56 PM 4/27/2009 -0500, Forrest Carpenter wrote:
>>>
>>>>All,
>>>>
>>>>
>>>>
>>>>Attached are the adobe AFM file, a png image and a CGM file showing 
>>>>characters drawn with a cap height of 71.8 mm. The characters included 
>>>>are the A-ring which shows the max y of 931 and the C-cedilla which has 
>>>>the min y of -225. The image was generated on UNIX using the Microcosm 
>>>>font for Helvetica which is visually and metrically equivalent to the 
>>>>Adobe font. When drawn on Windows mapping Helvetica to Arial we get 
>>>>different results.
>>>>
>>>>
>>>>
>>>>Regards,
>>>>
>>>>Forrest
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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